This invention relates generally to color cathode ray picture tubes, and is specifically addressed to an improved front assembly system for color tubes having shadow masks of the tensed foil type.
A color cathode ray tube typically includes three electron guns arranged in a delta or in-line configuration. Each gun projects an electron beam through the apertures of a shadow mask, also called a "color selection electrode," onto assigned target areas located on the inner surface of the faceplate. The target areas comprise a pattern of phosphor deposits typically arranged in groups of triads of dots or lines. Each of the triads consists of a deposit of a red-light-emitting, green-light emitting, and blue-light-emitting phosphor. To increase the apparent brightness of the display, and to minimize the incidence of color impurities which can result if a beam falls upon an unassigned phosphor deposit, the target area may include a layer of darkish light-absorbing material called a "grille" that surrounds and separates each of the dots or lines, and which serves as a guardband in case of beam misregistration. This type of screen is known as a "matrix screen" and "black surround" screen.
The area enclosed by the funnel and the shadow mask of a cathode ray tube is typically established as a field-free region for the excursion of the electron beams that selectively excite the pattern of phosphor deposits. The field-free region is established by charging certain inner components to a common high potential, typically in the range of 20-25 kilovolts. The components so charged typically include the conductive coating deposited on the inner surface of the funnel, and the shadow mask.
The phosphor deposits on the inner surface of the faceplate of the cathode ray tube are typically covered with a conductive film of aluminum. The aluminizing process comprises the deposition of an electron-pervious metallic film; that is, a film transparent to the flow of electrons comprising the three beams. The film increases the brightness of the display by acting as a mirror to reflect toward the viewer the visible light produced by the phosphors when activated by the electron beams. The film also carries the high-voltage charge to act as an electron-attractive ultor electrode for the display. The thickness of the film is typically about 2,000 Angstroms.
Stray magnetic fields can adversely affect the performance of color cathode ray tubes. The magnetic field of the earth is the primary offender. An unintercepted field can cause the electron beams to deviate from the normal landing area, resulting in color impurities. Terrestrial magnetic fields comprise paths of flux having both vertical and horizontal components. The flux path that has the greatest effect on beam landing is that which is transverse to the tube axis. Interception of most of the terrestrial magnetic flux can be accomplished by installing a magnetically permeable metallic shield either externally to the tube envelope, or internally. When installed internally, the shield is conventionally attached to the shadow mask, and extends rearwardly from the mask a predetermined distance into the tube envelope. The shield is usually designed so that, when in conjunction with the shadow mask, it completely encloses the major field-free excursion area of the electron beams, but it does not extend beyond the forward limit of the shadow mask.
The high potential required for tube operation is typically introduced into the tube envelope through an vacuum-tight electrical receptacle termed an anode button, the inner face of which is in contact with the conductive coating on the inner surface of the funnel. The potential on the funnel conductive coating is conveyed to the electron gun by spring means which extend from the forward electrode of the gun. The potential is also applied to the shadow mask, usually by spring means extending from the mask and in contact with the internal coating. The coating of electrically conductive aluminum on the phosphor deposits is also electrically charged. The electrical conduit from the electrically charged shadow mask to the aluminum coating is usually by means of a painted-on conductive "mustache" which is in contact with both the mask and the aluminum coating. lf there is an internal magnetic shield, it too may carry the high potential; the electrical conduit from the mask to the shield is usually by some form of spring means.
U.S. Pat. No. 3,894,321 to Moore, of common ownership herewith, is directed to a method for processing a color cathode ray tube having a thin foil mask sealed directly to the bulb. Included in the Moore disclosure is a description of the sealing of a foil mask between the juncture of the skirt of the faceplate and the funnel. The mask is shown as having two or more alignment holes near the corners of the mask which mate with alignment nipples in the faceplate. The nipples pass through the alignment holes to fit into recesses in the funnel. In another Moore embodiment, the front panel is shown as having a continuous ledge around the inner surface of the faceplate. The top surface of the ledge is spaced a Q-distance away from the faceplate for receiving the foil mask such that the mask is sealed within the tube envelope. In another embodiment, the ledges are two in number and located at the sides of the faceplate parallel with the y axis. An embodiment is also shown in which the faceplate is skirtless and essentially flat.
In U.S. Pat. No. 3,489,966 to Bradu et al., there is disclosed a cathode ray tube with a stainless steel post-focusing grid sealed between the sealing lands and the faceplate skirt and the funnel. The grid of wires is cut at the outer surface of the envelope, and an electrically conductive layer located on the exterior of the envelope coats the envelope zone which comprises the ends of the wires. A layer of sealing and insulative material laid over the conducting layer is said to provide for air-tightness and high-voltage integrity. The conductive layer also makes contact with a high-voltage connector for energizing the grid wires. In another configuration in which the high-voltage is applied to the screen the screen receives operating potential through a terminal which penetrates the faceplate skirt; this terminal in turn is connected to the screen by a conductive-paint layer.
A post-deflection cathode ray tube is disclosed in U.S. Pat. No. 3,502,942 to Kahn et al. A unitary color selection and focus-electrode assembly comprises a first electrode for color selection, and a second lens element formed as a mesh of electrical conductors. The color selection electrode and focus electrode assembly are insulated from each other, and each has a different potential thereon. The tube has two conductive coatings on the inside of the envelope, one of which is located on the internal surface of the funnel, but stops short of the plane of the electrode assembly. High voltage for beam acceleration is conducted to the coating through an anode button that penetrates the funnel. A flexible electrical conductor interconnects the color selection electrode with the funnel coating. The second coating is located on the inner surface of the faceplate skirt, and a high voltage for post-deflection focusing is conducted to the coating through a second anode button that penetrates the skirt. A separate spring-like connector projects from the PDF electrode to make contact with a second coating.
Barr in U.S. Pat. No. 3,541,373 discloses a cathode ray tube with a bifurcated spring bridging the shadow mask frame, and an internal conductive coating. The spring clips onto the rigid frame, or alternately, is welded to the shadow mask. The distal end makes contact with the inner conductive coating on the funnel which is electrically charged to a high potential. The novelty is said to lie in the bifurcation of the distal end, in which each of two independently operating tines has a different vibration frequency. The result is said to be a more shock-resistant connection and the avoidance of electrical interruption. Also, the positive contact is said to make possible the use of a weaker spring with reduced possibility of mechanical erosion of the conductive coating.
In Davis et al.--U.S. Pat. No. 3,898,510--there is set forth through-the-seal conductive means for traversing a CRT envelope seam to effect multiple connections therein. An internal spring-like conductive member straddles the seam at the junction of the funnel and the faceplate skirt to electrically connect the funnel internal conductive coating and the conductive coating on the screen. A conductive member extends through the seam to interconnect the conductive member with an external high voltage connector.
Marschka in U.S. Pat. No. 4,344,015 describes a screen contact means for a cathode ray tube. An anode button projecting through the funnel is attached to a screen contact assembly that conducts high voltage directly to the screen, while bridging the gap at which the funnel and faceplate are sealed together. A Nichrome foil member is placed beneath the screen contact point of the conductive member to serve as a non-abrading pad. A member attached transversely to the contact assembly provides for screen-pressure contact with the conductive coating on the inner surface of the funnel.
The following patents are also noted: 1,163,495 (GB); U.S. Pat. Nos. 2,761,990; 3,440,469; 3,638,063; 3,873,874; 3,894,321; 4,069,567; and 4,495,473.